Oscillation generator



April 1937- K. SCHLESINGER 2,077,269

050 ILLAT ION GENERATOR Filed April 14, 1933 Jwenfor;

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Patented Apr. 13, 1937 UNETE STATES PATENT OFIE Application April 14, 1933, Serial No. 666,125 In Germany April 15, 1932 8 Claims.

In the case of receiving circuits, more particularly according to the heterodyne principle, use is generally made of inductive feed-back, as in this connection the possibility is provided of coupling the frequency-determining oscillatory circuit so loosely with its associated oscillating tube that detuning of the circuit is avoided when changing tubes. It may also be readily accomplished in the case of these circuits that one plate of the tuning condenser of the oscillatory circuit be connected to earth, such as is absolutely essential for constructive reasons and for altering the wave range. Thedisadvantage of all of these circuits with inductive feed-back resides in the fact that for altering the wave change by changing the oscillatory coils switches are required which must have several contacts. "It is also not an entirely simple matter to obtain defined feed-back conditions on very short waves.

This advantage would be provided by the simple capacitative potential divider circuit. The same is also suitable even for the production of ultra-short waves, as the feed-back factor remains independent of frequency. There are, however, the following disadvantages: (1) no plate of the oscillatory circuit condenser is earthed, (2) the inner capacities of the tube are added strongly into the capacity of the oscillatory circuit, (3) all earth capacities at the tube and the oscillatory circuit enter into the feed-back factor and, under certain circumstances, if the same are sufiiciently large and unsymmetrical, may produce an interruption in the feed-back condition.

The invention sets forth means and circuits, by which the disadvantages referred to are completely eliminated, so that the capacitative feedback is capable of being employed for the generation of oscillations with graduated oscillation frequencies.

The invention relates further to the use of these circuits for heterodyne and superheterodyne receivers, and also sets forth input circuits for the generation of the intermediate frequency.

According to the invention, a potential divider circuit is employed in conjunction with indirectly heated tubes. The advantage of this arrangement resides in the fact that, as well known, it is possible in the case of indirectly heated tubes to build up a high-frequency potential between the cathode and earth. In this manner it is possible to earth dynamically both the filament as well as the grid of the tubes. Beyond this, it is also possible to earth the oscillatory circuit at one point, so that an arrangement is obtained having very considerable stability whilst avoiding detrimental and indefinite capacities.

In the accompanying drawing Figure 1 is a wiring diagram of an embodiment of the invention. Figures 2, 3 and 4 are wiring diagrams of modified circuit connections.

The fundamental circuit according to the invention is shown in Fig. 1. The condensers-3 and i are connected in series with the former connected between the anode I1 and cathode M, the later between the cathode I l and earth and both in shunt with the oscillatory circuit comprising the variable condenser l and inductance 2. The one side of the oscillatory circuit l, 2 is connected with the anode ll through the medium of a condenser- 5, whilst the other side is connected to earth. The filament l3 of the indirectly heated tube is connected with a heating current transformer ML The terminals H and I2 serve for the connection with the heating current source. and the terminals 8 and 9, which if necessary may be linked up through the medium of chokes 6 and l with the cathode l4 and the anode l1, serve for connection with the anode current source.

The grid-anode capacity in the case of this connection system enters fully into the frequency of the oscillatory circuit. This influence, in accordance with the invention, may be diminished by the use of screening grid tubes, the screening grid it of which is connected preferably dynamically, for example through the medium of a blocking condenser It, with the cathode IA. The source of signal modulations I9 is connected between the control grid I5 and earth in the usual manner.

The influence of the tube capacities on the oscillatory circuit, and accordingly the detuning, may be additionally decreased according to the invention by the inclusion of very small series capacities 2|], 2| (Fig. 2) between the potential divider condensers 3, 4 and the oscillatory circuit l, 2. The series capacities Zll, 2| may be selected, for example, so that they represent mere- 1y approximately 5% of the initial capacity of the rotating plate condenser l. Since, however, the feed-back condensers 3, 4 with approximately 40 cm. capacity are selected to be roughly ten times greater than the ordinary tube capacities, the detuning upon the removal of the tube amounts to only approximately .2%. Since, thirdly, the difference in capacity between two tubes of the same kind amounts only to a fraction of its own building-up capacity, the detuning which occurs when exchanging two tubes is so small as to ensure the operation of invariable, strictly tuned receivers.

When employing the circuit system according to the invention for superheterodyne receiving purposes, the antenna. circuit replaces the current source IS. A circuit of this nature is shown in Fig. 3. The aerial circuit 23 is coupled with the control grid l5, for example through the medium of a coil 22. The aerial and grid circuits may be formed as desired in the manner known per se.

In the anode circuit there may be inserted an oscillatory circuit, formed by a coil 24 and a condenser 25 and tuned to the intermediate frequency.

A further circuit system, which avoids the disadvantage of earthing by the switch elements situated in the anode circuit, is shown in Fig. 4. This circuit system differs from Fig. 3 principally by the fact that the circuit tuned to the intermediate frequency is disposed between cathode l4 and earth. The circuit tuned to the intermediate frequency is formed by the one potential divider condenser 4 and the coils 26, 21, whilst the oscillatory circuit is constituted by the coil 2 and the condensers l, 4, 2|. The condenser 3 in the case of this circuit system is very small in relation to the condenser 4. The ratio may be approximately 20:500.

The tuning-out condenser 20 is bridged by a high ohmic resistance 28, which should be selected as large as possible, but only insofar as this is permissible with consideration to the requisite anode current or anode potential. This connection system is also particularly suitable for short waves. As shown in Fig. 4, the selfinduction of the circuit tuned to the intermediate frequency is in this case divided into the coils 2 8, 21, in order to prevent a break in the oscillations, which as well known readily occurs-by frequencies which agree with harmonic vibrations of the natural oscillations of the large coil.

The circuits as described are possible forms of embodiment of the invention, which may be variously modified.

I claim:

1. In an oscillation generator an electronic tube having an anode, an indirectly heated cathode, and a control-grid, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back-coupling capacitative potential divider shunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a controlcurrent source inserted between said control-grid and earth for modulating the oscillations produced by said generator.

2. In an oscillation generator an electronic tube having an anode, an indirectly heated cathode, and a control-grid, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back-coupling capacitative potential divider shunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a controlcurrent source inserted between said control-grid and earth for modulating the oscillations produced by said generator, condensers of small capacity inserted between said high frequency circuit and said potential divider.

3. In a self-heterodyne receiver an oscillator generator and an electronic tube having an anode, an indirectly heated cathode, and a controlgrid, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit, consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back-coupling capacitative potential divider shunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a control-current source inserted between said control-grid and earth for modulating the oscillations produced by said generator, the input of the waves to be received being said control-current source, a circuit tuned to the intermediate frequency inserted in the anode connection of said tube.

4. In an oscillation generator an electronic tube having an anode, an indirectly heated cathode, and a control-grid, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back-coupling capacitative potential dividershunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a control-current source inserted between said control-grid and earth for modulating the oscillations produced by said generator, an intermediate-frequency circuit formed by a coil in parallel connection with the one condenser of said capacitive potential divider included between said cathode and the earthing point.

5. In an oscillation generator an electronic tube having an anode, an indirectly heated cathode, and a control grid, a screening gridconnected with said cathode by a condenser, the heating element of said cathode isolated from said cathode, a tunable frequency oscillatory circuit consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back-coupling capacitative potential divider shunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a control-current source inserted between said contro1-grid and earth for modulating the oscillations produced by said generator. I

6. In an oscillation generator an electronic tube having an anode, an indirectly heated cathode, and a control grid, a screening grid connected with said cathode by a condenser, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back-coupling capacitive potential divider shunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a control-current source inserted between said control-grid and earth for modulating the oscillations produced by said generator, condensers of 5 small capacity inserted between said high frequency circuit and said potential divider.

7. In a self-heterodyne receiver an oscillator generator and an electronic tube having an anode, an indirectly heated cathode, and a control-grid,

10 a screening grid connected with said cathode by a condenser, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit, consisting of a condenser and a coil in parallel, said circuit inserted 15 in series with a condenser between said anode and earth, a back-coupling capacitative potential divider shunted across the terminals of said coil consisting of two condensers in series, the middle point of which being connected to said cathode, a

20 source of direct current connected to said anode and said cathode, and a control-current source inserted between said control-grid and earth for modulating the oscillations produced by said generator, the input of the waves to be received being said control-current source, a circuit tuned to the intermediate frequency inserted in the anode connection of said tube.

8. In a self-heterodyne receiver an oscillator generator and an electronic tube having an anode, an indirectly heated cathode, and a control-grid, a screening grid connected with said cathode by a condenser, the heating element of said cathode isolated from said cathode, a tunable high frequency oscillatory circuit consisting of a condenser and a coil in parallel, said circuit inserted in series with a condenser between said anode and earth, a back -coupling capacitative potential divider shunted across the terminals of said coil consisting to two condensers in series, the middle point of which being connected to said cathode, a source of direct current connected to said anode and said cathode, and a control-current source inserted between said control-grid and earth for modulating the oscillations produced by said generator, condensers of small capacity inserted between said high frequency circuit and said potential divider.

KURT SCHLESINGER. 

